In the gas engine, an excessively high charge pressure leads to an increase in the pressure difference across the throttle valve, because the pressure required upstream of the cylinder head, or downstream of the throttle valve, for operation at constant power remains approximately constant.
If a threshold value of the pressure difference across the throttle valve is exceeded, the compressor of the turbocharger reaches the surge line. In the case of modern turbochargers with “narrow characteristic maps”, a very high pressure difference leads to “surging”. Surging refers to an instability in the volume flow rate delivered by the compressor, which in turn, due to other side-effects, can lead to system failures and to turbocharger damage and engine damage.
To avoid this, solutions are known which regulate the pressure difference across the throttle valve by using a bypass at the compressor or a bypass at the turbine of the turbocharger.
For example, an internal combustion engine having an exhaust-gas turbocharger is also already known from DE 103 15 148 A1. A bypass line or a bypass, which connects the primary side to the secondary side, is associated with the exhaust-gas turbocharger. To prevent surging of the compressor, it can be equipped with internal recirculation. Recirculation means that air or air mixture is recirculated from the secondary side of the compressor to the primary side of the compressor. This recirculation can also be configured in a switchable manner.
A device for a spark-ignition gas engine is known from DE 10 2009 049 394 A1, which device includes on the one hand a throttle valve as well as a detection unit for the pressure difference across the throttle valve, and on the other hand includes a throttle element in a bypass line of the exhaust-gas turbine for the purpose of regulating the volume flow rate in the bypass line.